Vacuum tube with ultrahigh frequency



Dec. 9, 1952 v. A. ALTOVSKY ETAL 2,621,304

VACUUM TUBE WITH ULTRAHIGH FREQUENCY Filed May 21, 1947 3 Sheets-Sheet 1I N V EN TOR .5' VLAD/Ml/P A. AUOKSA? GEO/P655 GQl/DET BY ATTORNEY Dec.9, 1952 v. A. ALTOVSKY El'AL 2,621,304

' VACUUM TUBE WITH ULTRAHIGH FREQUENCY Y m/M k ATTORNEY 5 v. A. ALTOVSKYETAL 2,621,304

VACUUM TUBE WITH ULTRAHIGH FREQUENCY Filed May 21, 1947 3 Sheets-Sheet 5INVENTORS VLAD/M/f? ,4. nzrarsxy GEORGES 600057 A T TORNZ'Y PatentedDec. 9, 1952 VACUUM TUBE WITH ULTRAHIGH FREQUENCY Vladimir ArcadieAltovsky and Georges-Goudet,. Paris, France, assignors to InternationalStandard Electric Corporation, New York, N. Y., a

corporation of Delaware Application May 21, 1947, Serial No. 749,514

In France September 19, 1944 Section 1, Public Law 690, August 8,1946Patent expires September .19., 1.964

4 Claims. (Cl. 315 -6 The present inventionrelates to" electron dis.-charge devices, particularly to ultra-high fre-'. quency devices of thekind in which the electrons of a beam are modulated in velocity.

A typical velocity-modulation tube comprises an electron beam source andtwo reentrant type cavity resonators. The beam is directed through thecentral opening of one resonator and hence through a metal cylinder,called a drift or slip tube, and finally through the central opening ofthe second resonator. When the resonators are excited, the electrons arealternately accelerated and retarded in the first cavity opening,causing them to be grouped into traveling bunches in the drift tube. Inthe second cavity opening the electron bunches give up energy to theoscillating field in the second cavity. For correct operation of thedevice, particularly as a self-excited generator of oscillations, acoupling is provided between the two resonators, which coupling may beloose or tight.

In the case of a loose coupling, it is necessary to exactly tune thenatural frequencies of the two cavity resonators. This makes themanufacture of the devices particularly difficult, because the cavityresonators must be made deformable or be provided with auxiliaryadjusting devices. On the other hand, in the case of a tight couplingbetween resonators it becomes unnecessary to tune the resonant volumesto the same frequency, and this makes their construction much easier.

From the viewpoint of intrinsic output of energy and the maximum powerthat canbe obtained from the device, it has been found that the highfrequency voltage applied to the modulation space of the first cavityopening must be less than the high frequency voltage applied to thepick-up space of the second cavity opening and that the ratio of thesevoltages must possess a quite definite value less than unity, dependingupon the order or mode of oscillation. The condition for maximum poweroutput is explained, for example, in an article by Clavier and LeBoiteux published in the Revue Generale de lElectricite, vol. 56, year1941, pages 109 ff.

In the case of tubes with tight coupling, it has so far not beenpossible to obtain the optimum voltage ratio at the two cavity openingsexcept with changes to the electron optical system that cletrimentallyaffect the speed modulation of the electrons. It has not beenpossible,heretofore, to obtain: thenecessary-diiference between the modulationand. pickup voltagesexcept by changing; the: geometric characteristicsof the modulation and pick-up spaces. The structure 2 then nolonger-operates under optimum conditions from the viewpoint of itsaction on the electron beam, and this brings about a loss of energywhich lessens the improvement that might other-I wise be expected;

The. object of the present invention consequently is an electrondis-charge device-ofthe velocity-modulation type which has the propergeometric relation of parts for best electron optics and. which providesthe optimum ratio of high frequency voltages at the two'cavity openingsfor maximum high frequency output power.

The two cavity resonators of the velocity-mod ulationdevice areeffectively combined according to one feature of this'inventi'on, in asingle cavity resonator so that the -modulating voltage and pick-upvoltage at the ends of the drift tube are tightly coupled and so thatthe modulating and pick-up frequencies are always synchronized. Yet, thesingle .cavity resonator, according to this invention, is asymmetricalwith respect to the opposite ends of the drift tube so as to apply thedesired voltages to the modulating and pickup openings.

These features, as well as others, are explained in detail in thefollowing description given with reference to the appended drawings, inwhich:

Fig. 1 illustrates schematically in longitudinal section aconventionalrelectrode structure for velocity modulators; with twotightly coupled cavity resonators. I

Fig. 2 illustratesschematically in longitudinal section an electrodestructureproviding the optimum geometric dimensions of parts for bestmodulation of .the electron beam and, associated, according to featuresof the invention, with a complex cavity having theresonance propertiesof a single cavity, and also, through its asymmetry, providing anoptimum ratio of modulation and pick-up voltages.

Figs. 3, 4, 5 and 6 illustrate schematically in section other examplesof arrangements of speed modulation tubes each with an asymmetricalcomplex cavity resonator, according to the basic features of theinvention, and

Figs. 7 and 8 illustrate a variant structure of an asymmetrical cavity,according to one feature of the invention, having a shape that is notone of revolution around the axis of the electron beam.

In conventional speed modulation tube ,strucv tures such as shown inFig. 1, the electrode. assembly is foundto be satisfactory for.modulation, of the electrons andfor pickingnptthe energy of themodulated beam. The structure consists of three tubes or cylindersegments I, 2 and 3 aligned along the path of an electron beam derivedat the cathode C and focused by electrode F. An accelerating electrode Amay be sealed in at the opposite end of the device. The conditions ofoptimum action on the beam are made possible by the dimensioning of thecylinder segments I, 2 and 3, and especially by the selection of theirdiameter cl, the lengths Z1 and Z2 of spaces 4 and 5 between segmentsI--2 and 2-3, respectively, and by the length 13 of cylinder 2. Space 4is called the modulation space, and space 5 is called the pick-up space,and electrode 2 is usually called the slip electrode or drift tube. Twocavity resonators 6 and T, which are symmetrical in known embodiments,are respectively coupled to the spaces 4 and 5 and serve as resonant oroscillatory circuits for the complete tube. The coupling between thesecavities is efiected by slots 8 in the middle wall 9, which is common tothe two resonators. If these slots are made of large size, the couplingbetween the volumes 6 and I will be tight, and this will make itpossible to dispense with devices for the precise adjustment of theresonance frequencies of the two resonators with respect to each other.

In tight coupled structures of this kind, it is apparent that the highfrequency voltage applied to the modulation space 4 will be, owing tothe structural symmetry of the parts equal to the high frequency pick-upvoltage applied to the pick-up space 5. The conditions of maximum poweroutput will consequently not be complied with. It is recognized in theinvention, however, that the use of a very tight coupling effected bylarge size slots 8, or even by the elimination of wall 9, makes itpossible to dispense with all necessity of symmetry. Contrary toexpectations, modification of the dimensions of the tube openings toobtain the mentioned optimum voltage ratio, does not result in a higheroutput. Unequal alteration of the values Z1, Z2 would change the actionof the electrode assembly I-23 on the electrons. The action on the beamwould then no longer be uniform in all the straight sections of the beamfrom the viewpoint of the high frequency fields, and the transit timesof the electrons would become incorrect for optimum operation of thetube.

In the tube of this invention, the electrode structure I-2-3 isdimensioned to provide optimum conditions of action on the beam,including proper electron transit times. A complex cavity resonatorhaving the resonance properties of a single cavity at the operatingfrequency is associated with the electrode structure I23 and is madeasymmetrical with respect to the modulation and pick-up spaces so as toobtain the optimum ratio of high frequency voltages that is necessaryfor obtaining maximum power output.

This complex cavity resonator, with asymmetrical distribution of thepotentials of the high frequency oscillations at the two cavityopenings, may be designed in various ways, particularly with astructural configuration that provides the desired effect. Figs. 2 and 3show two examples of complex cavity resonators of this kind associatedwith an electrode assembly I, 2 and 3 having electron optics for optimumaction on the beam. Corresponding parts are indicated by the samereference numbers as in Fig. 1.

In the example shown in Fig. 2, to the electrode assembly I, 2 and 3,there is associated a complex cavity resonator consisting of aconductive envelope I0 and a portion of conductive wall II shunting themodulation space. This wall portion II may even be reduced to a simpleconductive loop. Element II is given such shape and dimensions that theobtained complex cavity resonator, while having a single resonancefrequency in the selected range, provides an asymmetry of the modulationand pick-up high frequency voltages that is in the desired ratio.

The slip electrode 2 may, as shown in Fig. 2, be supported mechanicallyby the bridge element I I which may also serve as lead-in conductor forthis electrode. It is however evident that the slip electrode 2 may besupported and placed under voltage independently of element II of thecomplex volume.

In the embodiment shown in Fig. 3, the desired asymmetry of themodulating and pickup voltages is obtained by increasing the radial.dimensions of the opposing surfaces I2 and I3 that define the modulationspace 4 between electrodes I and 2. The walls of said electrodes. may bethickened as shown, or provided with out-turned flanges, to increase thedistance be-- tween the cavity and the beam in the drift tube, ascompared with the corresponding opposing surfaces of electrodes 2 and 3that define the pick-up space. The increased thickness of the wall I2I3reduces the voltage applied by the cavity to the beam.

Mechanical stability of the slip electrode 2 within the complex cavityresonator I4 may be effected by one or more stays of conductive orinsulating material. In case of insulating supports for electrode 2,separate voltages may be applied to the electrode by a connection wireI50. insulated in the wall of the cavity resonator I4, as shown in Fig.3. This arrangement makes it possible to employ slip electrode 2 as amodulation electrode of the wave produced by the oscillator.

In the embodiment shown in Fig. 4, the desired asymmetry is obtained bythe use of a sleeve H which is supported by or is integral with thecylinder segment I and which more or less completely caps or overliesthe modulation space while in Fig. 5, the sleeve I9 is supported by oris integral with the slip electrode 2. In either Fig. 4 or 5, the drifttube is supported by spokes 16 or I8. In Figs. 4 and 5, as in Fig. 3,the modulating space 4 is removed from the full intensity of the highfrequency electric field existmg in the cavity. The reduction in thefield in the modulating space 4, and the corresponding reduction of thepercentage of modulation of the electron velocities may be accuratelyadjusted to the optimum value by adjusting the length of the sleeve IIor I9. Such adjustments, according to this invention, require nocompromise with the best dimensions, Z1, Z2, 13 or d, Fig. l, of theoptical portion of the device.

The desired asymmetry of voltages at openings 4 and 5 may also beobtained by deforming the outer wall of the cavity resonator. In Fig. F,for example, the outer wall 2| has been constricted at 22 opposite themodulating space 4. 20 indicates support of the slip electrode 2, whichis shown here at the point of passage from one section to the other.

Use may be made of embodiments in which the complex cavity is alsoasymmetrical in shape around the mean axis of the beam. In Figs. 7 and8, for example, the peripheral wall 26 and the support 21 of the centralconduit 2 have been deformed asymmetrically with respect to themodulation and pick-up spaces. Further, the wall is flattened somewhatin the plane of the supports 21. In this example, the support is suchthat it delimits the slip channel. In Figs. '7 and 8, the axial lengthof tube 3 is quite short, being equal, approximately to the thickness ofthe wall.

Although the invention has been described with particular embodiments,it is evident that the invention is by no means limited thereto but, onthe contrary, is capable of numerous variants and adaptations in theconstruction of the asymmetrical complex cavity resonator in question.It is evident that numerous arrangements and shapes of the complexcavity resonators will provide the desired asymmetrical distribution ofthe high frequency potentials at the modulation and pick-up spaceswithout departing from the scope of the invention.

We claim:

1. An electron discharge device comprising three spaced and alignedmetal tubes, an electron gun disposed axially of said tubes forprojecting a beam of electrons therethrough, a single cavity resonatorcommunicating with the spaces between adjacent ends of said tubes, theelectrical dimensions of said metal tubes at one of said spaces beingdifferent from those at the other space for causing the high frequencyvoltages across said spaces to be unequal.

2. An electron velocity modulating device comprising metal wallsdefining a single cavity res onator with re-entrant portions and twospaced openings in said re-entrant portions, means mounted adjacent saidresonator for projecting a beam of electrons through said re-entrantportions successively past said openings, the walis of said resonator atone of said openings being 6 of different thicknesses from those at theother opening for producing unequal high frequency voltages at theopenings.

3. An electron velocity modulator comprising two cavity resonators, eachhaving re-entrant wall portions spaced apart and axially aligned for theprojection therethrough of an electron beam, the thicknesses of saidre-entrant wall portions at the spaces therebetween being different fromeach other to couple said cavity resonators unequally to the electronbeam, and said resonators being coupled together with suflicienttightness to insure synchronous operation thereof.

4. An electron velocity modulator comprising spaced and axially alignedmetal tubes, a metal envelope enclosing said tubes and formingresonators therewith communicating with the interior of said tubesthrough the spaces between adjacent ends thereof, and means mountedadjacent one of said spaces increasing the length in said onecommunicating passage between said resonator and the interior of saidmetal tubes.

VLADIMIR ARCADIE ALTOVSKY. GEORGES GOUDET.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,272,211 Kohler Feb. 10, 19422,289,952 Zworykin July 14, 1942 2,364,732 Ludi Dec. 12, 1944 2,405,611Samuel Aug. 13, 1946 2,466,064 Wathen et a1 Apr. 5, 1949 2,466,704Harrison Apr. 12, 1949

